The present invention relates generally to a pressure sensing and transmitting device.
Conventional pressure sensing and transmitting devices employ a pressure detecting device including a metal resistor member adhered on a surface of a metal diaphragm.
In the conventional devices, it has been considered to employ a ceramic as a diaphragm material to provide a longer life. Since a ceramic material does not easily make a plastic deformation, creep does not arise, even under a long period of a stress application, and a produced strain can be maintained constantly.
Further, as a resistor member that has a high gauge strain resistance variation sensitivity against a strain, it may be considered to employ a thick film resistor member such as described in "Changes in thick film resistor values due to substrate flexure announcement" (R. J. Holmes), published in Microelectronics and Reliability, Vol. 12, No. 4, issued October, 1973.
However, since a ceramic diaphragm has a very large Young's modulus, generation of strain due to a stress is small. Therefore, in a combination of a ceramic diaphragm with a thick film resistor member, it is difficult to obtain a large output with a thick film resistor member within a safe size range so that it will not break the ceramic diaphragm.
Furthermore, in order to combine a pressure detecting device which includes a thick resistor member secured to a ceramic diaphragm to form a pressure sensing and transmitting device, it is required to include some parts such as bolts, nuts and sealing materials for fixing the ceramic diaphragm to a housing of the pressure sensing and transmitting device. As a result, a boundary condition of the ceramic diaphragm is changed over a period of time by fatigue of said fixing parts. Therefore, there is a problem that long-term stability is not possible to compensate for.